Electric arc welding system

ABSTRACT

An electric arc welding system for creating an AC welding arc between an electrode and a workpiece wherein the system comprises a first controller for a first power supply to cause the first power supply to create an AC current between the electrode and workpiece by generating a switch signal or command with polarity reversing switching points in the first controller, with the first controller operated at first welding parameters in response to first power supply specific parameter signals to the first controller. The system has at least one slave controller for operating a slave power supply to create an AC current between the electrode and workpiece by reversing polarity of the AC current at switching points where the slave controller is operated at second welding parameters in response to second power supply specific parameter signals to the slave controller. An information network connected to the first controller and the slave controller and containing digital first and second power supply specific parameter signals for the first controller and the slave controller and a digital interface connects the first controller with the slave controller to control the switching points of said second power supply by the switch signal or command from the first controller.

This is application a continuation of pending U.S. application Ser. No.10/702,278, filed on Nov. 6, 2003, which is a continuation of U.S.application Ser. No. 10/236,836 now U.S. Pat. No. 6,660,966, filed onSep. 6, 2002, which is a continuation of U.S. application Ser. No.09/835,972 now U.S. Pat. No. 6,472,634, filed on Apr. 17, 2001, each ofwhich are incorporated herein by reference and owned by Assignee of thisapplication.

INCORPORATION BY REFERENCE INCORPORATION BY REFERENCE

The present invention is directed to an electric arc welding systemutilizing high capacity alternating circuit power supplies for drivingtwo or more tandem electrodes of the type used in seam welding of largemetal blanks. Although the invention can be used with any standard ACpower supply with switches for changing the output polarity, it ispreferred that the power supplies use the switching concept disclosed inStava U.S. Pat. No. 6,111,216 wherein the power supply is an inverterhaving two large output polarity switches with the arc current beingreduced before the switches reverse the polarity. Consequently, the term“switching point” is a complex procedure whereby the power supply isfirst turned off awaiting a current less than a preselected value, suchas 100 amperes. Upon reaching the 100 ampere threshold, the outputswitches of the power supply are reversed to reverse the polarity fromthe D.C. output link of the inverter. Thus, the “switching point” is anoff output command, known as a “kill” command, to the power supplyinverter followed by a switching command to reverse the output polarity.The kill output can be a drop to a decreased current level. Thisprocedure is duplicated at each successive polarity reversal so the ACpower supply reverses polarity only at a low current. In this manner,snubbing circuits for the output polarity controlling switches arereduced in size or eliminated. Since this switching concept is preferredto define the switching points as used in the present invention, StavaU.S. Pat. No. 6,111,216 is incorporated by reference. The concept of anAC current for tandem electrodes is well known in the art. Priorapplication Ser. No. 09/336,804 filed Jun. 12, 1999 discloses a systemwhereby tandem electrodes are each powered by a separate inverter typepower supply. The frequency is varied to reduce the interference betweenalternating current in the adjacent tandem electrodes. Indeed, thisapplication relates to single power sources for driving either a DCpowered electrode followed by an AC electrode or two or more AC drivenelectrodes. In each instance, a separate inverter type power supply isused for each electrode and, in the alternating current high capacitypower supplies, the switching point concept of Stava U.S. Pat. No.6,111,216 is employed. This system for separately driving each of thetandem electrodes by a separate high capacity power supply is backgroundinformation to the present invention and is incorporated herein as suchbackground. In a like manner, U.S. application Ser. No. 09/406,406 filedSep. 27, 1999 discloses a further arc welding system wherein eachelectrode in a tandem welding operation is driven by two or moreindependent power supplies connected in parallel with a single electrodearc. The system involves a single set of switches having two or moreaccurately balanced power supplies forming the input to the polarityreversing switch network operated in accordance with Stava U.S. Pat. No.6,111,216. Each of the power supplies is driven by a single commandsignal and, therefore, shares the identical current value combined anddirected through the polarity reversing switches. This type systemrequires large polarity reversing switches since all of the current tothe electrode is passed through a single set of switches. Thisapplication does show a master and slave combination of power suppliesfor a single electrode and discloses general background information towhich the invention is directed. For that reason, this application isalso incorporated by reference.

BACKGROUND OF INVENTION

Welding applications, such as pipe welding, often require high currentsand use several arcs created by tandem electrodes. Such welding systemsare quite prone to certain inconsistencies caused by arc disturbancesdue to magnetic interaction between two adjacent tandem electrodes. Asystem for correcting the disadvantages caused by adjacent AC driventandem electrodes is disclosed in prior application Ser. No. 09/336,804filed Jun. 21, 1999 by assignee of this invention. In that priorapplication, each of the AC driven electrodes has its own inverter basedpower supply. The output frequency of each power supply is varied so asto prevent magnetic interference between adjacent electrodes. Thissystem requires a separate power supply for each electrode. As thecurrent demand for a given electrode exceeds the current rating of theinverter based power supply, a new power supply must be designed,engineered and manufactured. Thus, such system for operating tandemwelding electrodes require high capacity or high rated power supplies toobtain high current as required for pipe welding. To decrease the needfor special high current rated power supplies for tandem operatedelectrodes, assignee developed the system disclosed in application Ser.No. 09/406,406 wherein each AC electrode is driven by two or moreinverter power supplies connected in parallel. These parallel powersupplies have their output current combined at the input side of apolarity switching network. Thus, as higher currents are required for agiven electrode, two or more parallel power supplies are used. In thissystem, each of the power supplies are operated in unison and shareequally the output current. Thus, the current required by changes in thewelding conditions can be provided only by the over current rating of asingle unit. A current balanced system did allow for the combination ofseveral smaller power supplies; however, the power supplies had to beconnected in parallel on the input side of the polarity reversingswitching network. As such, large switches were required for eachelectrode. Consequently, such system overcame the disadvantage ofrequiring special power supplies for each electrode in a tandem weldingoperation of the type used in pipe welding; but, there is still thedisadvantage that the switches must be quite large and the input,paralleled power supplies must be accurately matched by being drivenfrom a single current command signal. This prior application doesutilize the concept of a synchronizing signal for each welding celldirecting current to each tandem electrode. However, the system stillrequired large switches. This type of system was available for operationin an ethernet network interconnecting the welding cells. In ethernetinterconnections, the timing cannot be accurately controlled. In thesystem described, the switch timing for a given electrode need only beshifted on a time basis, but need not be accurately identified for aspecific time. Thus, the described system requiring balancing thecurrent and a single switch network has been the manner of obtaininghigh capacity current for use in tandem arc welding operations whenusing an ethernet network or an internet and ethernet control system.There is a desire to control welders by an ethernet network, with orwithout an internet link. Due to timing limitation, these networksdictated use of tandem electrode systems of the type using only generalsynchronizing techniques.

THE INVENTION

It is advantageous in high current systems for arc welding to drive oneelectrode with several paralleled inverter type power supplies whileaccommodating network control. The disadvantage has been that suchsystems required the current to be accurately balanced and required asingle high capacity output switching network. Such systems could becontrolled by a network; however, the parameter to each paralleled powersupply could not be varied. Each of the cells could only be offset fromeach other by a synchronizing signal. Such systems were not suitable forcentral control by the internet and/or local area network controlbecause an elaborate network to merely provide offset between cells wasnot advantageous.

The present invention utilizes the concept of a single AC arc weldingcell for each electrode wherein the cell itself includes one or moreparalleled power supplies each of which has its own switching network.The output of the switching network is then combined to drive theelectrode. This allows the use of relatively small switches for polarityreversing of the individual power supplies paralleled in the system. Inaddition, relatively small power supplies can be paralleled to build ahigh current input to each of several electrodes used in a tandemwelding operation. The use of several independently controlled powersupplies paralleled after the polarity switch network for driving asingle electrode allows advantageous use of a network, such as theinternet or ethernet.

In accordance with the invention, smaller power supplies in each systemare connected in parallel to power a single electrode. By coordinatingswitching points of each paralleled power supply with a high accuracyinterface, the AC output current is the sum of currents from theparalleled power supplies without combination before the polarityswitches. By using this concept, the ethernet network, with or withoutan internet link, can control the weld parameters of each paralleledpower supply of the welding system. The timing of the switch points isaccurately controlled by the novel interface, whereas the weldparameters directed to the controller for each power supply can beprovided by an ethernet network which has no accurate time basis. Thus,an internet link can be used to direct parameters to the individualpower supply controllers of the welding system for driving a singleelectrode. There is no need for a time based accuracy of these weldparameters coded for each power supply. In the preferred implementation,the switch point is a “kill” command awaiting detection of a currentdrop below a minimum threshold, such as 100 amperes. When each powersupply has a switch command, then they switch. The switch points betweenparallel power supplies, whether instantaneous or a sequence involving a“kill” command with a wait delay, are coordinated accurately by aninterface card having an accuracy of less than 10 μs and preferably inthe range of 1-5 μs. This timing accuracy coordinates and matches theswitching operation in the paralleled power supplies to coordinate theAC output current.

By using the internet or ethernet local area network, the set of weldparameters for each power supply is available on a less accurateinformation network, to which the controllers for the paralleled powersupplies are interconnected with a high accuracy digital interface card.Thus, the switching of the individual, paralleled power supplies of thesystem is coordinated. This is an advantage allowing use of the internetand local area network control of a welding system. The informationnetwork includes synchronizing signals for initiating several arcwelding systems connected to several electrodes in a tandem weldingoperation in a selected phase relationship. Each of the welding systemsof an electrode has individual switch points accurately controlled whilethe systems are shifted or delayed to prevent magnetic interferencebetween different electrodes. This allows driving of several ACelectrodes using a common information network. The invention isespecially useful for paralleled power supplies to power a givenelectrode with AC current. The switch points are coordinated by anaccurate interface and the weld parameter for each paralleled powersupply is provided by the general information network. This network canalso operate a DC electrode which does not require the interconnectedswitching points used in the present invention.

In accordance with the present invention, there is provided an electricarc welding system for creating an AC welding arc between the electrodeand workpiece. As will be explained, the system can drive one electrodeby a single inverter. As a feature of the system, two or more powersupplies can drive a single electrode. Thus, the system comprises afirst controller for a first power supply to cause the first powersupply to create an AC current between the electrode and workpiece bygenerating a switch signal with polarity reversing switching points ingeneral timed relationship with respect to a given system synchronizingsignal received by the first controller. This first controller isoperated at first welding parameters in response to a set of first powersupply specific parameter signals directed to the first controller.There is provided at least one slave controller for operating the slavepower supply to create an AC current between the same electrode andworkpiece by reversing polarity of the AC current at switching points.The slave controller operates at second weld parameters in response tothe second set of power supply specific parameter signals to the slavecontroller. An information network connected to the first controller andthe second or slave controller contains digital first and second powersupply specific parameter signals for the two controllers and the systemspecific synchronizing signal. Thus, the controllers receive theparameter signals and the synchronizing signal from the informationnetwork, which may be an ethernet network with or without an internetlink, or merely a local area network. The invention involves a digitalinterface connecting the first controller and the slave controller tocontrol the switching points of the second or slave power supply by theswitch signal from the first or master controller. In practice, thefirst controller starts a current reversal at a switch point. This eventis transmitted at high accuracy to the slave controller to start itscurrent reversal process. When each controller senses an arc currentless than a given number, a “ready signal” is created. After a “ready”signal from all paralleled power supplies, all power supplies reversepolarity. This occurs upon receipt of a strobe or look command each 25μs. Thus, the switching is in unison and has a delay of less than 25 μs.Consequently, both of the controllers have interconnected datacontrolling the switching points of the AC current to the singleelectrode. The same controllers receive parameter information and asynchronizing signal from an information network which in practicecomprises a combination of internet and ethernet or a local areaethernet network. In accordance with the invention, the timing accuracyof the digital interface is less than about 10 μs and, preferably, inthe general range of 1-5 μs. Thus, the switching points for the twocontrollers driving a single electrode are commanded within less than 5μs. Then, switching actually occurs within 25 μs. At the same time,relatively less time sensitive information is received from theinformation network also connected to the two controllers driving the ACcurrent to a single electrode in a tandem welding operation. The 25 μsmaximum delay can be changed, but is less than the switch commandaccuracy.

In accordance with another aspect of the present invention there isprovided an electrical arc welding system for creating an AC welding arcbetween an electrode and workpiece. The system comprises a first powersupply to create a first AC current with first weld parameters betweenthe electrode and workpiece by generating a first switch controllingsignal reversing polarity of the first current at a specific switchtime. A second power supply is provided to create a second AC currentwith second weld parameters between the same electrode and workpiece bya second switch controlling signal reversing polarity of the secondcurrent at a switch time coordinated with the specific switch time ofthe first power supply. The invention involves a timing interfacebetween the first and second power supplies to create the second switchreversing signal by the first switch reversing signal where the switchsignals are 10 μs and preferably less than 5 μs of the specific switchtime. Consequently, the paralleled individually switched power suppliesare coordinated by accurately matching the switch reversing times. Themaster controller has a switch command signal synchronized with a phasesignal. The command signal is transmitted rapidly by the digitalinterface to the controller of the paralleled power supply. The secondpower supply then processes its switch point. In one embodiment, theseswitch points cause the reversal of polarity. Preferably, these switchpoints merely cause the inverters to be “killed” so they decrease thecurrents by a time constant curve. When both currents are reduced belowa given amount, the paralleled power supplies switch.

In the invention, the interconnected controllers have a polarity logicindicating the polarity of the two output currents. This merely assuresthat the two power supplies are switched with matching polarities. Inthis manner, the controller of the first power supply tells thecontroller of the second power supply which polarity is being reversed.The polarity logic is not a part of the invention although it is used inimplementing the invention. The accuracy of the switching commands isthe critical aspect of the digital high speed interconnecting interfacebetween controllers that are otherwise controlled by an informationnetwork, such as an ethernet network with or without an internet link.

In accordance with still a further aspect of the invention, an electricarc welding system is provided for creating a first AC welding arcbetween a first weld electrode and a workpiece and a second AC weldingarc between a second weld electrode and the sane workpiece as the firstand second electrodes move along the workpiece. This is the definitionof a tandem mounted welding operation. The invention also comprises asystem including a first cell with at least two power supplies connectedto the first arc and operated at a first synchronized time determined bya first synchronized signal with first weld parameters and a highaccuracy interconnection interface between the power supplies of thefirst cell to correlate polarity switching of the power supplies in thefirst cell. There is also provided a second cell with at least two powersupplies connected to the second arc and operated at a secondsynchronized time determined by a second synchronized signal offset fromthe first synchronized signal with second weld parameters and a highaccuracy interconnection interface between the power supplies of thesecond cell to correlate polarity switching of the power supplies of thesecond cell. A low accuracy information network, such as an internetlink connected to a local area network, is connected to the first andsecond cells and contains digital signals including the first and secondweld parameters and digitized first and second synchronizing signals. Inthis manner, the paralleled power supplies of each cell areinterconnected by a high accuracy interface whereas the severalcontrollers are operated with signals in the information network thatare not time sensitive.

In one aspect of the invention, a power supply system for creating afirst AC signal and a second AC signal is provided. In one embodiment,the power supply system includes: a first system withat least two powersupplies operated at a first synchronized time determined by a firstsynchronized signal with first operation parameters and a high accuracyinterconnection interface between said power supplies of said firstsystem to correlate polarity switching of said power supplies of saidfirst system and a second system with at least two power suppliesoperated at a second synchronized time determined by a secondsynchronize signal offset from said first synchronize signal with secondoperation parameters and a high accuracy interconnection interfacebetween said power supplies of said second system to correlate polarityswitching of said power supplies of said second system. In thisembodiment, each power supply includes: a center tapped inductor with afirst portion creating a first polarity where said corresponding ACsignal is positive and a second portion creating a second polarity wheresaid corresponding AC signal is negative, a first switch for routingsaid corresponding AC signal through said first portion of saidinductor, and a second switch for routing said corresponding AC signalthrough said second portion of said inductor.

In another embodiment, the power supply system includes: a first systemwith at least two power supplies operated at a first synchronized timedetermined by a first synchronized signal with first operationparameters and a high accuracy interconnection interface between saidpower supplies of said first system to correlate polarity switching ofsaid power supplies of said first system and a second system with atleast two power supplies operated at a second synchronized timedetermined by a second synchronize signal offset from said firstsynchronize signal with second operation parameters and a high accuracyinterconnection interface between said power supplies of said secondsystem to correlate polarity switching of said power supplies of saidsecond system. In this embodiment, each power supply includes an outputswitching network. The output switching network includes: a first switchin series with a first inductor segment creating a first polarityassociated with said corresponding AC signal that is positive when saidfirst switch is turned on, a second switch in series with a secondinductor segment creating a second polarity associated with saidcorresponding AC signal that is negative when said second switch isturned on, and control means for alternately turning said first switchon and said second switch off at a first switch reversing point andturning said second switch on and said first switch off at a secondswitch reversing point to create the corresponding AC signal.

In another aspect of the invention, a power supply system is provided.In one embodiment, the power supply system includes: a first controllerfor a first power supply to cause said first power supply to create anAC current by generating a switch signal with polarity reversingswitching points in a general timed relationship with respect to a givensystem specific synchronizing signal to said first controller, saidfirst controller operated at first parameters in response to first powersupply specific parameter signals to said first controller and at leastone slave controllerfor operating a slave power supply to create an ACcurrent by reversing polarity of said AC current at switching points,said slave controller operated at second parameters in response tosecond power supply specific parameter signals to said slave controller.In this embodiment, the first power supply and each slave power supplyinclude: a center tapped inductor with a first portion creating a firstpolarity where said corresponding AC current is positive and a secondportion creating a second polarity where said corresponding AC currentis negative, a first switch for muting said corresponding AC currentthrough said first portion of said inductor, and a second switch forrouting said corresponding AC current through said second portion ofsaid inductor.

In another embodiment, the power supply system includes: a firstcontroller for a first power supply to cause said first power supply tocreate an AC current by generating a switch signal with polarityreversing switching points in a general timed relationship with respectto a given system specific synchronizing signal to said firstcontroller, said first controller operated at first parameters inresponse to first power supply specific parameter signals to said firstcontroller and at least one. slave controller for operating a slavepower supply to create an AC current by reversing polarity of said ACcurrent at switching points, said slave controller operated at secondparameters in response to second power supply specific parameter signalsto said slave controller. In this embodiment, the first powersupply andeach slave power supply include an output switching network. The outputswitching network includes: a first switch in series with a firstinductor segment creating a first polarity associated with saidcorresponding AC current that is positive when said first switch isturned on, a second switch in series with a second inductor segmentcreating a second polarity associated with said corresponding AC currentthat is negative when said second switch is turned on, and control meansfor alternately turning said first switch on and said second switch offat a first switch reversing point and turning said second switch on andsaid first switch off at a second switch reversing point to create thecorresponding AC current.

In still another embodiment, the power supply system includes: at leasta first power supply for delivering a first low frequency current and asecond power supply for delivering a second low frequency current. Inthis embodiment, each of said power supplies include: a three phasevoltage input operated at line frequency, a rectifier to convert saidinput voltage to a DC voltage link and a high frequency switching typeinverter converting said DC voltage link to a high frequency AC current,an output rectifier circuit to provide a positive voltage terminal and anegative voltage terminal, and an output switching network operated at agiven low frequency for directing a pulsating current at said given lowfrequency from said terminals. The output switching network includes: acenter tapped inductor with a first portion creating a first polaritywhere said corresponding pulsating current is positive and a secondportion creating a second polarity where said corresponding pulsatingcurrent is negative, a first switch for routing said correspondingpulsating current through said first portion of said inductor, and asecond switch for routing said corresponding pulsating current throughsaid second portion of said inductor.

In yet another embodiment, the power supply system includes: at least afirst power supply for delivering a first low frequency current and asecond power supply for delivering a second low frequency current. Inthis embodiment, each of said power supplies include: a three phasevoltage input operated at line frequency, a rectifier to convert saidinput voltage to a DC voltage link and a high frequency switching typeinverter converting said DC voltage link to a high frequency AC current,an output rectifier circuit to provide a positive voltage terminal and anegative voltage terminal, and an output switching network operated at agiven low frequency for directing a pulsating current at said given lowfrequency from said terminals. The output switching network includes: afirst switch in series with a first inductor segment creating a firstpolarity associated with said corresponding pulsating current that ispositive when said first switch is turned on, a second switch in serieswith a second inductor segment creating a second polarity associatedwith said corresponding pulsating current that is negative when saidsecond switch is turned on, and control means for alternately turningsaid first switch on and said second switch off at a first switchreversing point and turning said second switch on and said first switchoff at a second switch reversing point to create the correspondingpulsating current.

In still another aspect of the invention, an electric arc welding systemfor creating an AC welding arc between an electrode and a workpiece isprovided. In one embodiment, the electric arc welding system includes: afirst power supply to create a first AC current with first weldparameters between said electrode and workpiece by generating a firstswitch controlling signal reversing polarity of said first current at aspecific switch time and a second power supply to create a second ACcurrent with second weld parameters between said electrode and workpieceby a second switch controlling signal reversing polarity of said secondcurrent at a switch time near said specific switch time. In thisembodiment, the first and second power supplies each include: a centertapped inductor with a first portion creating a first polarity wheresaid corresponding AC current is positive and a second portion creatinga second polarity where said corresponding AC current is negative, afirst switch for routing said corresponding AC current through saidfirst portion of said inductor, and a second switch for routing saidcorresponding AC current through said second portion of said inductor.

In another embodiment, the electric arc welding system includes: a firstpower supply to create a first AC current with first weld parametersbetween said electrode and workpiece by generating a first switchcontrolling signal reversing polarity of said first current at aspecific switch time and a second power supply to create a second ACcurrent with second weld parameters between said electrode and workpieceby a second switch controlling signal reversing polarity of said secondcurrent at a switch time near said specific switch time. In thisembodiment, the first and second power supplies each include an outputswitching network. The output switching network includes: a first switchin series with a first inductor segment creating a first polarityassociated with said corresponding AC current that is positive when saidfirst switch is turned on, a second switch in series with a secondinductor segment creating a second polarity associated with saidcorresponding AC current that is negative when said second switch isturned on, and control means for alternately turning said first switchon and said second switch off at a first switch reversing point andtuming said second switch on and said first switch off at a secondswitch reversing point to create the corresponding AC current.

In still another embodiment, the electric arc welding system includes: afirst power supply to create a first AC current with first weldparameters between said electrode and workpiece by generating a firstswitch signal for reversing polarity of said first current at a specifictime and a second power supply to create a second AC current with secondweld parameters between said electrode and workpiece by a second switchsignal for reversing polarity of said second current at a given time. Inthis embodiment, the first and second power supplies each include: acenter tapped inductor with a first portion creating a first polaritywhere said corresponding AC current is positive and a second portioncreating a second polarity where said corresponding AC current isnegative, a first switch for routing said corresponding AC currentthrough said first portion of said inductor, and a second switch forrouting said corresponding AC current through said second portion ofsaid inductor.

In yet another embodiment, the electric arc welding system includes: afirst power supply to create a first AC current with first weldparameters between said electrode and workpiece by generating a firstswitch signal for reversing polarity of said first current at a specifictime and a second power supply to create a second AC current with secondweld parameters between said electrode and workpiece by a second switchsignal for reversing polarity of said second current at a given time. Inthis embodiment, the first and second power supplies each include anoutput switching network. The output switching network includes: a firstswitch in series with a first inductor segment creating a first polarityassociated with said corresponding AC current that is positive when saidfirst switch is turned on, a second switch in series with a secondinductor segment creating a second polarity associated with saidcorresponding AC current that is negative when said second switch isturned on, and control means for alternately turning said first switchon and said second switch off at a, first switch reversing point andturning said second switch on and said first switch off at a secondswitch reversing point to create the corresponding AC current.

In yet still another embodiment, the electric arc welding systemincludes: a first power supply to create a first AC current with firstweld parameters between said electrode and workpiece by generating afirst switch controlling signal reversing polarity of said first currentat a specific active switch time and a second power supply to create asecond AC current with second weld parameters between said electrode andworkpiece by a second switch controlling signal reversing polarity ofsaid second current at a switch activate time. In this embodiment, thefirst and second power supplies each include: a center tapped inductorwith a first portion creating a first polarity where said correspondingAC current is positive and a second portion creating a second polaritywhere said corresponding AC current is negative, a first switch forrouting said corresponding AC current through said first portion of saidinductor, and a second switch for routing said corresponding AC currentthrough said second portion of said inductor.

In another embodiment, the electric arc welding system includes: a firstpower supply to create a first AC current with first weld parametersbetween said electrode and workpiece by generating a first switchcontrolling signal reversing polarity of said first current at aspecific active switch time and a second power supply to create a secondAC current with second weld parameters between said electrode andworkpiece by a second switch controlling signal reversing polarity ofsaid second current at a switch activate time. In this embodiment, thefirst and second power supplies each include an output switchingnetwork. The output switching network includes: a first switch in serieswith a first inductor segment creating a first polarity associated withsaid corresponding AC current that is positive when said first switch isturned on, a second switch in series with a second inductor segmentcreating a second polarity associated with said corresponding AC currentthat is negative when said second switch is turned on, and control meansfor alternately turning said first switch on and said second switch offat a first switch reversing point and turning said second switch on andsaid first switch off at a second switch reversing point to create thecorresponding AC current. In yet another aspect of the invention, anelectric welder is provided. In one embodiment, the electric welderincludes: a first power source with a first 6 output polarity changingswitch network creating a first AC output with first output leadsconnected across an electrode and a workpiece and a second power sourcewith a second output polarity changing switch network creating a secondAC output with second output leads connected across said electrode andworkpiece in parallel with said first leads. In this embodiment, thefirst and second output polarity changing switch networks each include:a center tapped inductor with a first portion creating a first polaritywhere said corresponding AC output is positive and a second portioncreating a second polarity where said corresponding AC output isnegative, a first switch for routing said corresponding AC outputthrough said first portion of said inductor, and a second switch forrouting said corresponding AC output through said second portion of saidinductor.

In another embodiment, the electric welder includes: a first powersource with a first output polarity changing switch network creating afirst AC output with first output leads connected across an electrodeand a workpiece and a second power source with a second output polaritychanging switch network creating a second AC output with second outputleads connected across said electrode and workpiece in parallel withsaid first leads. In this embodiment, the first and second outputpolarity changing switch networks each include: a first switch in serieswith a first inductor segment creating a first polarity associated withsaid corresponding AC output that is positive when said first switch isturned on, a second switch in series with a second inductor segmentcreating a second polarity associated with said corresponding AC outputthat is negative when said second switch is turned on, and control meansfor alternately turning said first switch on and said second switch offat a first switch reversing point and turning said second switch on andsaid first switch off at a second switch reversing point to create thecorresponding AC output.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of the preferred embodiment of the presentinvention;

FIG. 2 is a wiring diagram of two paralleled power supplies, each ofwhich include a switching output which power supplies are used inpracticing the invention;

FIG. 3 is a pictorial view showing three tandem operated electrodes eachof which is driven by a welding system of the present invention with theoffset synchronizing signals from the information network shown in thegraph of FIG. 3A and using the general schematic diagram of FIG. 3B;

FIG. 4 is a block diagram showing in more detail the preferredembodiment of the present invention to operate two separate weldingsystems or cells from a single central control;

FIG. 5 is a schematic layout of the invention used to drive severaltandem electrodes as shown in the pictorial view of FIG. 5A;

FIG. 6 is a schematic layout of the invention used for driving twotandem electrodes as shown pictorially in FIG. 6A;

FIG. 7 is a pictorial view showing two tandem mounted electrodesoperated by offset switching operation shown in the graphs of FIG. 7Ausing the switch point concept of Stava U.S. Pat. No. 6,111,216; and,

FIG. 8 is a schematic layout of the software program to cause switchingof the paralleled power supplies as soon as the coordinated switchcommands have been processed and the next coincident signal has beencreated.

PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only and not forthe purpose of limiting same, in FIG. 1 there is a single electric arcwelding system S in the form of a single cell to create an alternatingcurrent as an arc at weld station WS. This system or cell includes afirst master welder A with output leads 10, 12 in series with electrodeE and workpiece W in the form of a pipe seam joint or other weldingoperation. Hall effect current transducer 14 provides a voltage in line16 proportional to the current of welder A. Less time critical data,such as welding parameters, are generated at a remote central control18. In a like manner, a slave following welder B includes leads 20, 22connected in parallel with leads 10, 12 to direct an additional ACcurrent to the weld station WS. Hall effect current transducer 24creates a voltage in line 26 representing current levels in welder Bduring the welding operation. Even though a single slave or followerwelder B is shown, any number of additional welders can be connected inparallel with master welder A to produce an alternating current acrosselectrode E and workpiece W. A novel feature is the combining of ACcurrent at the weld station instead of prior to a polarity switchingnetwork. Each welder would include a controller and inverter based powersupply illustrated as a combined master controller and power supply 30and a slave controller and power supply 32. In accordance with theinvention, controllers 30, 32 receive parameter data and synchronizationdata from a relatively low level logic network. The parameterinformation or data is power supply specific whereby each of the powersupplies is provided with the desired parameters such as current,voltage and/or wire feed speed. A low level digital network can providethe parameter information; however, the advantage of the inventionrelates to the ability to parallel several controller and power supplyunits having AC output currents in a manner that the switching of the ACcurrent for polarity reversal occurs at the same time. The “same” timeindicates a time difference of less than 10 μs and preferably in thegeneral range of 1-5 μs. To accomplish precise coordination of the ACoutput from power supply 30 and power supply 32, the switching pointsand polarity information can not be provided from a general logicnetwork wherein the timing is less precise. Thus, in accordance with theinvention, the individual AC power supplies are coordinated by highspeed, highly accurate DC logic interface referred to as “gateways.” Asshown in FIG. 1, power supplies 30, 32 are provided with the necessaryoperating parameters indicated by the bidirectional leads 42 m, 42 s,respectively. This non-time sensitive information is provided by adigital network shown in FIG. 1 and to be described later. Master powersupply 30 receives a synchronizing signal as indicated by unidirectionalline 40 to time the controllers operation of its AC output current. Thepolarity of the AC current for power supply 30 is outputted as indicatedby line 46. The actual switching command for the AC current of masterpower supply 30 is outputted on line 44. The switch command tells powersupply S, in the form of an inverter, to “kill,” which is a drasticreduction of current. In an alternative, this is actually a switchsignal to reverse polarity. The “switching points” or command on line 44preferably is a “kill” and current reversal commands utilizing the“switching points” as set forth in Stava U.S. Pat. No. 6,111,216. Thus,timed switching points or commands are outputted from power supply 30 byline 44. These switching points or commands may involve a power supply“kill” followed by a switch ready signal at a low current or merely acurrent reversal point. The switch “ready” is used when the “kill”concept is implemented because neither inverters are to actually reverseuntil they are below the set current. The polarity of the switches ofcontroller 30 controls the logic on line 46. Slave power supply 32receives the switching point or command logic on line 44 b and thepolarity logic on line 46 b. These two logic signals are interconnectedbetween the master power supply and the slave power supply through thehighly accurate logic interface shown as gateway 50, the transmittinggateway, and gateway 52, the receiving gateway. These gateways arenetwork interface cards for each of the power supplies so that the logicon lines 44 b, 46 b are timed closely to the logic on lines 44, 46,respectively. In practice, network interface cards or gateways 50, 52control this logic to within 10 μs and preferably within 1-5 μs. Theinvention involves a low accuracy network controlling the individualpower supplies for data from central control 18 through lines 42 m, 42s, illustrated as provided by the gateways or interface cards. Theselines contain data from remote areas (such as central control 18) whichare not time sensitive and do not use the accuracy characteristics ofthe gateways. The highly accurate data for timing the switch reversaluses interconnecting logic signals through network interface cards 50,52. The system in FIG. 1 is a single cell for a single AC arc.

The invention is primarily applicable for tandem electrodes wherein twoor more AC arcs are created to fill the large gap found in pipe welding.Thus, the master power supply 30 receives a synchronization signal whichdetermines the timing or phase operation of the system S for a singleelectrode, i.e. ARC 1.

System S is used with other identical systems to generate ARCs 2, 3, and4. This concept is schematically illustrated in FIGS. 5 and 6. Thesynchronizing or phase setting signals are shown in FIG. 1 with only oneof the tandem electrodes. An information network N comprising a centralcontrol computer and/or web server 60 provides digital information ordata relating to specific power supplies in several systems or cellscontrolling different electrodes in a tandem operation. Internetinformation is directed to a local area network in the form of anethernet network 70 having local interconnecting lines 70 a, 70 b, 70 c.Similar interconnecting lines are directed to each power supply used inthe four cells creating ARCs 1, 2, 3 and 4 of a tandem weldingoperation. The description of system or cell S applies to each of thearcs at the other electrodes. If AC current is employed, a master powersupply is used. In some instances, merely a master power supply is usedwith a cell specific synchronizing signal. A single arc weldinginstallation will not require synchronizing signals. If higher currentsare required, the systems or cells include a master and slave powersupply combination as described with respect to system S of FIG. 1. Insome instances, a DC arc is preferred, such as the leading electrode ina tandem electrode welding operation. A DC power supply need not besynchronized, nor is there a need for accurate interconnection of thepolarity logic and switching points or commands. Some DC poweredelectrodes may be switched between positive and negative, but not at thefrequency of an AC driven electrode. Irrespective of the make-up of thearcs, ethernet or local area network 70 includes the parameterinformation identified in a coded fashion designated for specific powersupplies of the various systems used in the tandem welding operation.This network also employs synchronizing signals for the several cells orsystems whereby the systems can be offset in a time relationship. Thesesynchronizing signals are decoded and received by a master power supplyas indicated by line 40 in FIG. 1. In this manner, the AC arcs areoffset on a time basis. These synchronizing signals are not required tobe as accurate as the switching points through network interface cardsor gateways 50, 52. Synchronizing signals on the data network arereceived by a network interface in the form of a variable pulsegenerator 80. The generator creates offset synchronizing signals inlines 84, 86 and 88. These synchronizing signals dictate the phase ofthe individual alternating current cells for separate electrodes in thetandem operation. Synchronizing signals can be generated by interface 80or actually received by the generator through the network 70. Inpractice, network 70 merely activates generator 80 to create the delaypattern for the many synchronizing signals. Also, generator 80 can varythe frequency of the individual cells by frequency of the synchronizingpulses if that feature is desired in the tandem welding operation.

A variety of controllers and power supplies could be used for practicingthe invention as described in FIG. 1; however, preferred implementationof the invention is set forth in FIG. 2 wherein power supply PSA iscombined with controller and power supply 30 and power supply PSB iscombined with controller and power supply 32. These two units areessentially the same in structure and are labeled with the same numberswhen appropriate. Description of power supply PSA applies equally topower supply PSB. Inverter 100 has an input rectifier 102 for receivingthree phase line current L1, L2, and L3. Output transformer 110 isconnected through an output rectifier 112 to tapped inductor 120 fordriving opposite polarity switches Q1, Q2. Controller 140 a of powersupply PSA and controller 140 b of PSB are essentially the same, exceptcontroller 140 a outputs timing information to controller 140 b.Switching points or lines 142, 144 control the conductive condition ofpolarity switches Q1, Q2 for reversing polarity at the time indicated bythe logic on lines 142, 144, as explained in more detail in Stava U.S.Pat. No. 6,111,216 incorporated by reference herein. The control isdigital with a logic processor; thus, A/D converter 150 converts thecurrent information on feedback line 16 or line 26 to controllingdigital values for the level of output from error amplifier 152 which isillustrated as an analog error amplifier. In practice, this is a digitalsystem and there is no further analog signal in the controlarchitecture. As illustrated, however, amplifier has a first input 152 afrom converter 150 and a second input 152 b from controller 140 a or 140b. The current command signal on line 152 b includes the wave shaperequired for the AC current across the arc at weld station WS. Theoutput from amplifier 152 is converted to an analog voltage signal byconverter 160 to drive pulse width modulator 162 at a frequencycontrolled by oscillator 164, which is a timer program in the processorsoftware. This frequency is greater than 18 kHz. The total architectureof this system is digitized in the preferred embodiment of the presentinvention and does not include reconversion back into analog signal.This representation is schematic for illustrative purposes and is notintended to be limiting of the type of power supply used in practicingthe present invention. Other power supplies could be employed.

Implementation of the present invention is by driving separateelectrodes in a tandem welding process with AC current creating thewelding arc at the individual electrodes. Such a tandem arrangement isillustrated in FIGS. 3, 3A, and 3B wherein workpiece W is in the form ofspaced edges of plates 200, 202 to define a longitudinal gap 204.Electrodes 210, 212 and 214 are melted by AC arcs to deposit beads 210a, 212 a and 214 a, respectively. Each of the arcs, 1, 2 and 3 has adifferent phase relationship from information received through network Nas shown in FIG. 1. Specific digital synchronizing signals 220, 222 and224 are offset by distances X and Y shown in FIG. 3A, and havefrequencies x, y, and z. These frequencies may be the same or different.These electrode or cell specific synchronizing signals are communicatedto the various cells from central control 60 through internet 62 to thephase generator 80, as shown in FIG. 1. The individual synchronizingpulses are directed through lines 82, 84 and 86 for controlling thetiming and/or frequency of the individual welding cells for theelectrodes 210, 212 and 214. In practice, the leading electrode mayinvolve use a DC arc, which need not be synchronized. Further, thesynchronizing signals 220, 222 and 224 can be in phase. Eachsynchronizing signal sets the timing of the individual welding systemsor cells as shown in FIG. 1.

FIG. 4 shows a general layout illustrating the present invention whenused for two cells S′, S″ or two arc formed by electrodes E₁ andworkpiece W₁ and electrode E₂ and workpiece W₂. In practice, theworkpieces are both identical and only the electrodes are separate;however, they do define separate arcs in the welding process. To use thepresent invention for the two arcs as shown in FIG. 4, network 300includes a central control 302 to which is loaded power supply specificparameters as indicated by interface block 304. These parameters arestored as indicated by block 306 for interrogation by network 300whenever desired. The network server is connected through internet 310to the local area network 312 from which weld parameters are loaded intothe individual control and power supply combinations M₁, S₁, M₂, and S₂through interconnections illustrated as lines 320-326. In a like manner,the synchronizing signals for the individual systems S′, S″ areavailable on network 312 and are communicated as illustrated as line 330with the pulse generator or clock 340. The output of the generator isrepresented as synchronizing data lines 332, 334 for individuallycontrolling the delay or synchronization of systems S′, S″. Thisdictates the time relationship between the two arcs of the dualelectrode system shown in FIG. 4. Cell S′ includes master power supplyM₁ connected in parallel with slave power supply S₁. In a like manner,system S″ includes master M₂ connected in parallel with the output ofslave power supply S₂. Network interface cards 342, 344 communicate thetiming from the master to the slave and directs the polarity logic asindicated with respect to the disclosure shown in FIG. 1. In thismanner, two separate electrodes used in tandem are driven separatelywith the parameters and synchronizing signals being directed through anetwork which can include an internet link. Actual implementation of atiming block control is located inside the master control board. Theinterface card S′, S″ translates and isolates the signals between themaster control and the slave control.

The invention can be expanded to include any number of electrodes. Threeelectrodes 350, 352 and 354 are shown in FIGS. 5 and 5A. Network 360 aspreviously described communicates with system S shown in FIG. 1 togetherwith two additional systems 370, 372. Network 360 controls the logic toand through gateways 50 and 52 shown in FIG. 1 together with similargateways 380 and 382 for systems 370, 372, respectively. This embodimentof the invention illustrates two power supplies PSA and PSB forproviding synchronized and timed AC current through one electrode 356.Electrode 352 is connected with network 360 by gateway 380 so powersupply PSC uses only a single master to produce an AC current forelectrode 352. Electrode 354 is driven by power supply PSD which is a DCpower supply without output polarity switches and is driven throughgateway 382 by network 360. Other arrangements are used to constructarchitecture of different tandem electrodes process. For instance, twoelectrodes 400,402 are shown in the layout of FIGS. 6 and 6A. Fourseparate power supplies PSA₁, PSB₁, PSC₁, and PSD₁ are connected inparallel to produce an AC current across electrode 402. Power supply PSEis a DC power supply without output polarity switches. All of the powersupplies are provided with individual gateways or network interfacecards 410, 412, 414, 416 and 418, respectively. Each of the gatewaysreceives parameters for the individual power supplies. Gateways 410-416are interconnected to assure that the timing and polarity of theswitches in the first four power supplies are correlated accurately.Although gateways 414,416 are indicated to be driven in series withgateway 412, in practice, they are driven directly from the output ofgateway 410 in parallel fashion. This prevents the stacking of timingdifferences in the individual gateways.

As indicated, the switching points of the master and slave powersupplies are really a switching sequence wherein the inverter is firstturned off and then the switches are reversed to change the polarityafter the power supply reaches a low current. When the inverter isturned off, the current is reduced. Then reversal of polarity iseffected. This concept is shown in Stava U.S. Pat. No. 6,111,216. Thispatented switching technique is disclosed in FIGS. 7 and 7A, wherein twoelectrodes 420, 422 having AC current curves schematically illustratedas curve 424 and curve 426. In curve 424, the power supply is turned offat point 430. The current decays to a low current level 432 at whichtime there is a reversal to a negative polarity. This negative currentlevel is maintained until the desired parameter has been reached. Thepower supply is then turned off at point 434 and the negative currentpulse decays to switch point 436 at which time the switches reverse to apositive polarity. With a master and one or more slave power supplies,it is necessary to coordinate the kill points 430, 434, as well as theswitch points or times 432, 436. For simplicity, this polarity reversalsequence is referred to as the “switching time.” Curve 426 is offset bythe distance e and is provided by one or more power supplies connectedin series. This curve has power supply kill point 440 and kill point444. The switching points 442,446 correspond with the current reversalswitching points 432, 436. Even though the technique set forth in FIG.7A is preferred, a direct current reversal at the switching points isalso used with the present invention. In that instance, the switchesmust be larger and require a snubber network or a larger snubber networkin parallel with the switches.

As indicated, when the master controller is to switch, a switch commandis issued to the master controller. This causes a “kill” signal to bereceived by the master so a kill signal and polarity logic is rapidlytransmitted to the controller of one or more slave power suppliesconnected in parallel with a single electrode. If standard AC powersupplies are used with large snubbers in parallel with the polarityswitches, the slave controller or controllers are immediately switchedwithin 1-10 μs after the master power supply receives the switchcommand. This is the advantage of the high accuracy interface cards orgateways. In practice, the actual switching for current reversal of theparalleled power supplies is not to occur until the output current isbelow a given value, i.e. about 100 amperes. This allows use of smallerswitches.

The implementation of the invention using this delayed switchingtechnique requires the actual switch only after all power supplies arebelow the given low current level. The delay process is accomplished inthe software of the digital processor and is illustrated by theschematic layout of FIG. 8. When the controller of master power supply500 receives a command signal as represented by line 502, the powersupply starts the switching sequence. The master outputs a logic on line504 to provide the desired polarity for switching of the slaves tocorrespond with polarity switching of the master. In the commandedswitch sequence, the inverter of master power supply 500 is turned offor down so current to electrode E is decreased as read by hall effecttransducer 510. The switch command in line 502 causes an immediate“kill” signal as represented by line 512 to the controllers ofparalleled slave power supplies 520,522 providing current to junction530 as measured by hall effect transducers 532, 534. All power suppliesare in the switch sequence with inverters turned off or down. Softwarecomparator circuits 550, 552, 554 compare the decreased current to agiven low current referenced by the voltage on line 556. As each powersupply decreases below the given value, a signal appears in lines 560,562, and 564 to the input of a sample and hold circuits 570, 572, and574, respectively. The circuits are outputted by a strobe signal in line580 from each of the power supplies. When a set logic is stored in acircuit 570, 572, and 574, a YES logic appears on lines READY¹, READY²,and READY³ at the time of the strobe signal. This signal is generated inthe power supplies and has a period of 25 μs; however, other high speedstrobes could be used. The signals are directed to controller C of themaster power supply, shown in dashed lines in FIG. 8. A software ANDingfunction represented by AND gate 580 has a YES logic output on line 582when all power supplies are ready to switch polarity. This outputcondition is directed to clock enable terminal ECLK of software flipflop 600 having its D terminal provided with the desired logic of thepolarity to be switched as appearing on line 504. An oscillator or timeroperated at about 1 MHz clocks flip flop by a signal on line 602 toterminal CK. This transfers the polarity command logic on line 504 to aQ terminal 604 to provide this logic in line 610 to switch slaves 520,522 at the same time the identical logic on line 612 switches masterpower supply 500. After switching, the polarity logic on line 504 shiftsto the opposite polarity while master power supply awaits the nextswitch command based upon the switching frequency. Other circuits can beused to effect the delay in the switching sequence; however, theillustration in FIG. 8 is the present scheme.

The interface timing is disclosed as less than 10 μs. This value is tobe substantially more accurate than the ethernet accuracy. Thus, it canbe as high as about 100 μs and still provide an advantage. But,coordinated switching is facilitated with an accuracy of less than about10 μs with a READY strobe at 25 μs. Each power supply is ready to switchpolarity before the switch command is generated. One can reduce beforethe ready current and then come back up while the other is reducing tothe ready current. The key is accurate control and switching at lowcurrent. In addition, the power supplies could be back-to-back reversepolarity choppers with the positive state of the reverse polaritychopper switch by the accurate interface. A back-to-back AC chopperpower supply is shown in prior U.S. application Ser. No. 09/575,264,filed May 22, 2000 and incorporated by reference herein.

1. A power supply system for creating a first AC signal and a second ACsignal, said system comprising: a first system for creating said firstAC signal with at least two power supplies operated at a firstsynchronized time determined by a first synchronized signal with firstoperation parameters and a high accuracy interconnection interfacebetween said power supplies of said first system to correlate polarityswitching of said power supplies of said first system; wherein eachpower supply in said first system includes: a center tapped inductorwith a first portion creating a first polarity where said first ACsignal is positive and a second portion creating a second polarity wheresaid first AC signal is negative; a first switch for routing said firstAC signal through said first portion of said inductor; and a secondswitch for routing said first AC signal through said second portion ofsaid inductor; and a second system for creating said second AC signalwith at least two power supplies operated at a second synchronized timedetermined by a second synchronize signal offset from said firstsynchronize signal with second operation parameters and a high accuracyinterconnection interface between said power supplies of said secondsystem to correlate polarity switching of said power supplies of saidsecond system; wherein each power supply in said second system includes:a center tapped inductor with a first portion creating a first polaritywhere said second AC signal is positive and a second portion creating asecond polarity where said second AC signal is negative; a first switchfor routing said second AC signal through said first portion of saidinductor; and a second switch for routing said second AC signal throughsaid second portion of said inductor.
 2. The power supply system setforth in claim 1, further comprising: a low accuracy information networkconnected to said first and second systems and containing digitalsignals including said first and second operational parameters anddigitized first and second synchronize signals.
 3. A power supply systemfor creating a first AC signal and a second AC signal, said systemcomprising: a first system for creating said first AC signal with atleast two power supplies operated at a first synchronized timedetermined by a first synchronized signal with first operationparameters and a high accuracy interconnection interface between saidpower supplies of said first system to correlate polarity switching ofsaid power supplies of said first system; wherein each power supply insaid first system includes an output switching network, the outputswitching network comprising: a first switch in series with a firstinductor segment creating a first polarity associated with said first ACsignal that is positive when said first switch is turned on; a secondswitch in series with a second inductor segment creating a secondpolarity associated with said first AC signal that is negative when saidsecond switch is turned on; and control means for alternately turningsaid first switch on and said second switch off at a first switchreversing point and turning said second switch on and said first switchoff at a second switch reversing point to create at least a portion ofthe first AC signal; and a second system for creating said second ACsignal with at least two power supplies operated at a secondsynchronized time determined by a second synchronize signal offset fromsaid first synchronize signal with second operation parameters and ahigh accuracy interconnection interface between said power supplies ofsaid second system to correlate polarity switching of said powersupplies of said second system; wherein each power supply in said secondsystem includes an output switching network, the output switchingnetwork comprising: a first switch in series with a first inductorsegment creating a first polarity associated with said second AC signalthat is positive when said first switch is turned on; a second switch inseries with a second inductor segment creating a second polarityassociated with said second AC signal that is negative when said secondswitch is turned on; and control means for alternately turning saidfirst switch on and said second switch off at a first switch reversingpoint and turning said second switch on and said first switch off at asecond switch reversing point to create at least a portion of the secondAC signal.
 4. The power supply system set forth in claim 3, furthercomprising: a low accuracy information network connected to said firstand second systems and containing digital signals including said firstand second operational parameters and digitized first and secondsynchronize signals.
 5. The power supply system set forth in claim 3wherein said inductor segments of each power supply are a part of asingle inductor within each corresponding power supply.
 6. An electricarc welding system for creating an AC welding arc between an electrodeand a workpiece, said system comprising: a first power supply to createa first AC current with first weld parameters between said electrode andworkpiece by generating a first switch controlling signal reversingpolarity of said first current at a specific switch time; and a secondpower supply to create a second AC current with second weld parametersbetween said electrode and workpiece by a second switch controllingsignal reversing polarity of said second current at a switch time nearsaid specific switch time; wherein the first and second power supplieseach include: a center tapped inductor with a first portion creating afirst polarity where said corresponding AC current is positive and asecond portion creating a second polarity where said corresponding ACcurrent is negative; a first switch for routing said corresponding ACcurrent through said first portion of said inductor; and a second switchfor routing said corresponding AC current through said second portion ofsaid inductor.
 7. The electric arc welding system set forth in claim 6,further comprising: a timing interface between said first and secondpower supplies to create said second signal in relation to said firstsignal.
 8. The electric arc welding system set forth in claim 6, furthercomprising: a timing interface between said first and second powersupplies to create said second signal by said first signal where saidswitch time of said second power supply is within about 5 μs of saidspecific switch time.
 9. An electric arc welding system for creating anAC welding arc between an electrode and a workpiece, said systemcomprising: a first power supply to create a first AC current with firstweld parameters between said electrode and workpiece by generating afirst switch controlling signal reversing polarity of said first currentat a specific switch time; and a second power supply to create a secondAC current with second weld parameters between said electrode andworkpiece by a second switch controlling signal reversing polarity ofsaid second current at a switch time near said specific switch time;wherein the first and second power supplies each include an outputswitching network, the output switching network comprising: a firstswitch in series with a first inductor segment creating a first polarityassociated with said corresponding AC current that is positive when saidfirst switch is turned on; a second switch in series with a secondinductor segment creating a second polarity associated with saidcorresponding AC current that is negative when said second switch isturned on; and control means for alternately turning said first switchon and said second switch off at a first switch reversing point andturning said second switch on and said first switch off at a secondswitch reversing point to create the corresponding AC current.
 10. Theelectric arc welding system set forth in claim 9, further comprising: atiming interface between said first and second power supplies to createsaid second signal in relation to said first signal.
 11. The electricarc welding system set forth in claim 9, further comprising: a timinginterface between said first and second power supplies to create saidsecond signal by said first signal where said switch time of said secondpower supply is within about 5 μs of said specific switch time.
 12. Theelectric arc welding system set forth in claim 9 wherein said inductorsegments of each first and second power supply are a part of a singleinductor within each corresponding power supply.
 13. An electric arcwelding system for creating an AC welding arc between an electrode and aworkpiece, said system comprising: a first power supply to create afirst AC current with first weld parameters between said electrode andworkpiece by generating a first switch signal for reversing polarity ofsaid first current at a specific time; and a second power supply tocreate a second AC current with second weld parameters between saidelectrode and workpiece by a second switch signal for reversing polarityof said second current at a given time; wherein the first and secondpower supplies each include: a center tapped inductor with a firstportion creating a first polarity where said corresponding AC current ispositive and a second portion creating a second polarity where saidcorresponding AC current is negative; a first switch for routing saidcorresponding AC current through said first portion of said inductor;and a second switch for routing said corresponding AC current throughsaid second portion of said inductor.
 14. The electric arc weldingsystem set forth in claim 13, further comprising: a timing interfacebetween said first and second power supplies to create said secondsignal by said first signal.
 15. The electric arc welding system setforth in claim 14, further comprising: a circuit to switch said powersupplies after said first and second signal.
 16. The electric arcwelding system set forth in claim 15, said circuit comprising: adetector to switch said power supplies when the current of said powersupplies is less than a given amount.
 17. The electric arc weldingsystem set forth in claim 13, further comprising: a timing interfacebetween said first and second power supplies to create said secondsignal by said first signal where said given time of said second powersupply is within about 10 μs of said specific time of said first powersupply.
 18. An electric arc welding system for creating an AC weldingarc between an electrode and a workpiece, said system comprising: afirst power supply to create a first AC current with first weldparameters between said electrode and workpiece by generating a firstswitch signal for reversing polarity of said first current at a specifictime; and a second power supply to create a second AC current withsecond weld parameters between said electrode and workpiece by a secondswitch signal for reversing polarity of said second current at a giventime; wherein the first and second power supplies each include an outputswitching network, the output switching network comprising: a firstswitch in series with a first inductor segment creating a first polarityassociated with said corresponding AC current that is positive when saidfirst switch is turned on; a second switch in series with a secondinductor segment creating a second polarity associated with saidcorresponding AC current that is negative when said second switch isturned on; and control means for alternately turning said first switchon and said second switch off at a first switch reversing point andturning said second switch on and said first switch off at a secondswitch reversing point to create the corresponding AC current.
 19. Theelectric arc welding system set forth in claim 18, further comprising: atiming interface between said first and second power supplies to createsaid second signal by said first signal.
 20. The electric arc weldingsystem set forth in claim 19, further comprising: a circuit to switchsaid power supplies after said first and second signal.
 21. The electricarc welding system set forth in claim 20, said circuit comprising: adetector to switch said power supplies when the current of said powersupplies is less than a given amount.
 22. The electric arc weldingsystem set forth in claim 18, further comprising: a timing interfacebetween said first and second power supplies to create said secondsignal by said first signal where said given time of said second powersupply is within about 10 μs of said specific time of said first powersupply.
 23. The electric arc welding system set forth in claim 18wherein said inductor segments of each first and second power supply area part of a single inductor within each corresponding power supply. 24.An electric arc welding system for creating an AC welding arc between anelectrode and a workpiece, said system comprising: a first power supplyto create a first AC current with first weld parameters between saidelectrode and workpiece by generating a first switch controlling signalreversing polarity of said first current at a specific active switchtime; and a second power supply to create a second AC current withsecond weld parameters between said electrode and workpiece by a secondswitch controlling signal reversing polarity of said second current at aswitch activate time; wherein the first and second power supplies eachinclude: a center tapped inductor with a first portion creating a firstpolarity where said corresponding AC current is positive and a secondportion creating a second polarity where said corresponding AC currentis negative; a first switch for routing said corresponding AC currentthrough said first portion of said inductor; and a second switch forrouting said corresponding AC current through said second portion ofsaid inductor.
 25. The electric arc welding system set forth in claim24, further comprising: a timing interface between said first and secondpower supplies to create said second signal by said first signal wheresaid first and second signals are within about 10 μs.
 26. The electricarc welding system set forth in claim 24, further comprising: a timinginterface between said first and second power supplies to create saidsecond signal by said first signal.
 27. The electric arc welding systemset forth in claim 26, further comprising: a circuit to switch saidpower supplies after said first and second signal.
 28. The electric arcwelding system set forth in claim 27, said circuit comprising: adetector to switch said power supplies when the current of said powersupplies is less than a given amount.
 29. An electric arc welding systemfor creating an AC welding arc between an electrode and a workpiece,said system comprising: a first power supply to create a first ACcurrent with first weld parameters between said electrode and workpieceby generating a first switch controlling signal reversing polarity ofsaid first current at a specific active switch time; and a second powersupply to create a second AC current with second weld parameters betweensaid electrode and workpiece by a second switch controlling signalreversing polarity of said second current at a switch activate time;wherein the first and second power supplies each include an outputswitching network, the output switching network comprising: a firstswitch in series with a first inductor segment creating a first polarityassociated with said corresponding AC current that is positive when saidfirst switch is turned on; a second switch in series with a secondinductor segment creating a second polarity associated with saidcorresponding AC current that is negative when said second switch isturned on; and control means for alternately turning said first switchon and said second switch off at a first switch reversing point andturning said second switch on and said first switch off at a secondswitch reversing point to create the corresponding AC current.
 30. Theelectric arc welding system set forth in claim 29, further comprising: atiming interface between said first and second power supplies to createsaid second signal by said first signal where said first and secondsignals are within about 10 μs.
 31. The electric arc welding system setforth in claim 29, further comprising: a timing interface between saidfirst and second power supplies to create said second signal by saidfirst signal.
 32. The electric arc welding system set forth in claim 31,further comprising: a circuit to switch said power supplies after saidfirst and second signal.
 33. The electric arc welding system set forthin claim 32, said circuit comprising: a detector to switch said powersupplies when the current of said power supplies is less than a givenamount.
 34. The electric arc welding system set forth in claim 29wherein said inductor segments of each first and second power supply area part of a single inductor within each corresponding power supply. 35.An electric welder, comprising: a first power source with a first outputpolarity changing switch network creating a first AC output with firstoutput leads connected across an electrode and a workpiece; and a secondpower source with a second output polarity changing switch networkcreating a second AC output with second output leads connected acrosssaid electrode and workpiece in parallel with said first leads; whereinthe first and second output polarity changing switch networks eachinclude: a center tapped inductor with a first portion creating a firstpolarity where said corresponding AC output is positive and a secondportion creating a second polarity where said corresponding AC output isnegative; a first switch for routing said corresponding AC outputthrough said first portion of said inductor; and a second switch forrouting said corresponding AC output through said second portion of saidinductor.
 36. The electric arc welding system set forth in claim 35wherein the current from said power sources is added.
 37. An electricwelder, comprising: a first power source with a first output polaritychanging switch network creating a first AC output with first outputleads connected across an electrode and a workpiece; and a second powersource with a second output polarity changing switch network creating asecond AC output with second output leads connected across saidelectrode and workpiece in parallel with said first leads; wherein thefirst and second output polarity changing switch networks each include:a first switch in series with a first inductor segment creating a firstpolarity associated with said corresponding AC output that is positivewhen said first switch is turned on; a second switch in series with asecond inductor segment creating a second polarity associated with saidcorresponding AC output that is negative when said second switch isturned on; and control means for alternately turning said first switchon and said second switch off at a first switch reversing point andturning said second switch on and said first switch off at a secondswitch reversing point to create the corresponding AC output.
 38. Theelectric arc welding system set forth in claim 37 wherein the currentfrom said power sources is added.
 39. The electric arc welding systemset forth in claim 37 wherein said inductor segments of each first andsecond output polarity changing switch network are a part of a singleinductor within each corresponding output polarity changing switchnetwork.